Why is the image not transparent in when I import as a plane?
If you imported your image by first creating an image plane (Add &gt; Image &gt; Background), then you will want to click on the resulting plane object in Object Mode, and then look in the Object Data tab of the Properties Panel to find its Opacity slider.

If you created it as a Background Image, you will want to select your camera instead (this is easiest to do in the Outliner window), and then look in the same Object Data tab from the Properties Panel, which will now show the object data for the camera. This will expose you to a different opacity slider.

Hope this helps.